This disclosure relates to sol-gel processes used to form photoconducting imaging members. More specifically, the present disclosure relates to a photoreceptor layer, and in particular, a charge transport layer, formed by sol-gel processes.
In the art of xerography, also known as electrostatographic or electrophotographic printing, a xerographic plate or drum, known as a photoreceptor or imaging member, comprising a photoconductive insulating layer is imaged by first uniformly depositing an electrostatic charge on the imaging surface of the photoreceptor and then exposing the photoreceptor to a pattern of activating electromagnetic radiation such as light or a laser source, which selectively dissipates the charge in the illuminated areas of the plate while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles or toner particles on the imaging surface.
Generally, layered photoresponsive imaging members are described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the entire disclosure of which is incorporated herein by reference, wherein there is illustrated an imaging member comprised of a photogenerating layer, and an aryl amine hole transport layer. For example, charge transport layers comprised of aryl diamines dispersed in polycarbonates, like MAKROLON® are known. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent can comprise resins that are substantially incapable of transporting for any significant distance, injected charge carriers generated by the photoconductive particles.
There are also disclosed in U.S. Pat. No. 3,871,882 photoconductive substances comprised of specific perylene-3,4,9,10-tetracarboxylic acid derivatives. In accordance with the teachings of this patent, the photoconductive layer is preferably formed by vapor depositing the perylene derivatives in a vacuum. Also, there is specifically disclosed in this patent dual layer photoreceptors with perylene-3,4,9,10-tetracarboxylic acid diimide derivatives, which have spectral response in the wavelength region of from 400 to 600 nanometers. Further, in U.S. Pat. No. 4,555,463, the entire disclosure of which is incorporated herein by reference, there is illustrated a layered imaging member with a chloroindium phthalocyanine photogenerating layer. In U.S. Pat. No. 4,587,189, the entire disclosure of which is incorporated herein by reference, there is illustrated a layered imaging member with a nonhalogenated perylene pigment photogenerating component. Both of the aforementioned patents disclose an aryl amine component as a hole transport layer and wherein there can be selected a resin binder.
Moreover, there are disclosed in U.S. Pat. No. 4,419,427 electrographic recording media with a photosemiconductive double layer comprised of a first layer containing charge carrier perylene diimide pigments, and a second layer with one or more compounds which are charge transporting materials when exposed to light.
U.S. Pat. No. 4,419,427 discloses the use of highly-loaded dispersions of peryiene bisimides, with bis(2,6-dichlorophenylimide) being a preferred material, in binder resins as charge generating layers in devices overcoated with a charge transporting layer such as a poly(vinylcarbazole) composition. U.S. Pat. No. 4,429,029 illustrates the use, in devices similar to those of the '427 patent, of bisimides and bisimidazo perylenes in which the perylene nucleus is halogenated, preferably to an extent where 45 to 75 percent of the perylene ring hydrogens have been replaced by halogen. U.S. Pat. No. 4,587,189, the entire disclosure of which is incorporated herein by reference, illustrates layered photoresponsive imaging members prepared with highly-loaded dispersions or, preferably, vacuum evaporated thin coatings of cis- and trans-bis(benzimidazo)perylene (4a, X=1,2-phenylene) and other perylenes overcoated with hole transporting compositions comprised of a variety of N,N,N′,N′-tetraaryl-4,4′-diaminobiphenyls. U.S. Pat. No. 4,937,164 illustrates the use of perylene bisimides and bisimidazo pigments in which the 1,12-and/or 6,7 position of the perylene nucleus is bridged by one or two sulfur atoms wherein the pigments in the charge generating layers are either vacuum evaporated or dispersed in binder resins and a layer of tetraaryl biphenyl hole transporting molecules.
In U.S. Pat. No. 4,869,988 and U.S. Pat. No. 4,946,754, the entire disclosures of which are incorporated herein by reference, there are described layered photoconductive imaging members with transport layers incorporating, for example, biarylyl diarylamines, N,N-bis(biarylyl)anilines, and tris(biarylyl)amines as charge transport compounds. In the above-mentioned patents, there are disclosed improved layered photoconductive imaging members comprised of a supporting substrate, a photogenerating layer optionally dispersed in an inactive resinous binder, and in contact therewith a charge transport layer comprised of the above-mentioned charge transport compounds, or mixtures thereof dispersed in resinous binders.
It is also indicated in the aforementioned patents that there may be selected as resin binders for the charge transport molecules those components as illustrated in U.S. Pat. No. 3,121,006 including polycarbonates, polyesters, epoxy resins, polyvinylcarbazole; and also wherein for the preparation of the charge transport layer with a polycarbonate there is selected methylene chloride as a solvent.
Organic photoreceptors, i.e., photoreceptors that utilize organic compounds in the charge generation and/or charge transport layers (CTL), have recently been used to provide improved performance. Such organic photoreceptors typically provide improved performance in terms of better charge acceptance, wider spectral sensitivity, lower cost, and easier manufacture. However, such organic photoreceptors also generally exhibit decreased performance in terms of shorter operating life due primarily to increased wear and scratch rates. For example, a charge transport layer may be doped with polytetrafluoruethylene (PTFE) and/or silica. Charge transport layers incorporating such additives do exhibit improved wear resistance and, thus, an extended photoreceptor life. These systems, however, are dispersions, as opposed to a homogenous solution, and exhibit problems with dispersion stability, and/or materials loss issues. Consequently, doping the charge transport layer with PTFE and/or silica may deteriorate the electrical properties, print quality (PQ) and other system performance of the charge transport layer and/or the photoreceptor, which prevents such CTL systems from satisfying the long-life requirements needed for electrostatographic imaging systems.
Cross-linked CTL systems are also known to exhibit improved wear resistance and, thus, extend photoreceptor life. However, cross-linked CTL systems also deteriorate the electrical properties and cannot fully satisfy the PQ and long-life requirements needed for electrostatographic imaging systems.
Although imaging members with various charge transport layers, especially hole transport layer materials with hole transport molecules including the aryl amines dispersed in resinous binders such as polycarbonates, have been disclosed in the art, and are suitable for their intended purposes, a need remains for improving imaging members, particularly layered members, with chemically and mechanically robust transport layers. Further, there continues to be a need for layered imaging members wherein the layers are sufficiently adhered to one another to allow the continuous use of such members in repetitive imaging systems without layer separation. A further need resides in the provision of photoconductive imaging members with desirable mechanical characteristics. One or more of these and other needs may be accomplished, it is believed, in the embodiments disclosed herein.